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Formation of an

aDepartment of Physics and the Astronomy

University, Seoul 05006, KoreabDepartment of Physics, Riphah Institute of

Riphah International University, 14 Ali Road

riphah.edu.pkcDepartment of Physics, College of Science, M

Zul 11932, Saudi Arabia

† Electronic supplementary informa10.1039/c8ra09656b

Cite this: RSC Adv., 2019, 9, 10017

Received 23rd November 2018Accepted 18th March 2019

DOI: 10.1039/c8ra09656b

rsc.li/rsc-advances

This journal is © The Royal Society of C

MoTe2 based Schottky junctionemploying ultra-low and high resistive metalcontacts†

Sikandar Aftab,a Muhammad Waqas Iqbal, *b Amir Muhammad Afzal,a

M. Farooq Khan,a Ghulam Hussain,b Hafiza Sumaira Waheedb

and Muhammad Arshad Kamran c

Schottky-barrier diodes have great importance in powermanagement andmobile communication because

of their informal device technology, fast response and small capacitance. In this research, a p-type

molybdenum ditelluride (p-MoTe2) based Schottky barrier diode was fabricated using asymmetric metal

contacts. The MoTe2 nano-flakes were mechanically exfoliated using adhesive tape and with the help of

dry transfer techniques, the flakes were transferred onto silicon/silicon dioxide (Si/SiO2) substrates to

form the device. The Schottky-barrier was formed as a result of using ultra-low palladium/gold (Pd/Au)

and high resistive chromium/gold (Cr/Au) metal electrodes. The Schottky diode exhibited a clear

rectifying behavior with an on/off ratio of �103 and an ideality factor of �1.4 at zero gate voltage. In

order to check the photovoltaic response, a green laser light was illuminated, which resulted in

a responsivity of �3.8 � 103 A W�1. These values are higher than the previously reported results that

were obtained using conventional semiconducting materials. Furthermore, the barrier heights for Pd and

Cr with a MoTe2 junction were calculated to be 90 meV and 300 meV, respectively. In addition, the

device was used for rectification purposes revealing a stable rectifying behavior.

1. Introduction

Because of their unique semiconductive characteristics, tran-sition metal dichalcogenides (TMDs), have been used forextensive applications in nanoelectronics such as photodetec-tors,1–3 and spin-eld effect transistors.4 The TMDs have a bandgap of around 1 to 2 eV,5,6 and demonstrate fascinating elec-trical and optical properties.7–10 Molybdenum ditelluride(MoTe2) can be reduced to a monolayer or a few layers from itsbulk form using adhesive tape through mechanical exfolia-tion.10 As found from previous reports, MoTe2 in its bulk formshows an indirect band gap of 0.88 eV, whereas its monolayerhas a direct band-gap of 1.02 eV.8,11,12 The mobility for few-layered MoTe2 lies in the range of 0.2–40 cm2 V�1 s�1.13–16

Furthermore, use of MoTe2 has been shown to be favorable formany applications in environmental sensing, light emittingdiodes and photosensors.17,18

and Graphene Research Institute, Sejong

Computing and Applied Sciences (RICAS),

, Lahore, Pakistan. E-mail: waqas.iqbal@

ajmaah University, PO Box No. 1712, Al-

tion (ESI) available. See DOI:

hemistry 2019

The two-dimensional (2D) material-based junctions haveshown outstanding properties such as optical absorption,charge transportation and band alignment for optoelectronicand electronic applications.19,20 Until now, the study has mainlybeen based on heterojunctions comprising p–n junctions forpractical uses of 2D materials, however semiconductor/metalSchottky barrier diodes (SBD) have not been studied exten-sively.21,22 The SBD is formed by a contact effect of metal anda semiconductive material which is the simplest structureamongst modern electronic devices.23 The SBDs have beenshown to be promising for applications in electronic devices, forexample, as photodiodes, power diodes, sensors, and integratedcircuits.24,25 Schottky-barrier diodes have great importance inpower management and mobile communications because oftheir informal device technology, fast response and smallcapacitance.26,27 In particular, Schottky diodes are majoritycarrier devices and because they are single carrier devices, theyhave advantages because of the junction diode which isa bipolar-device.

The interface properties of metal and semiconductor areinuenced by the conductivity type of the charge carrier. Themetal and semiconductor interface be either a rectifying type oran ohmic type, and is roughly dependent on the work functionvalues of them. For example, a semiconductor material with n-type conductivity would show rectifying behavior with metalshaving greater work function values and show ohmic behavior

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with those having low work function values. However, semi-conductors with p-type conductivity exhibit the opposite char-acteristics. The Schottky barrier because of a difference of Fermilevel of the semiconductor and the work function of the metal,play an important role to determine the performance ofa diode.28–30

In this research, the MoTe2 based eld effect transistor (FET)is formed by using asymmetric metals contacts chromium/gold(Cr/Au) and palladium/gold (Pd/Au) to understand the chargecarrier transport and the interface characteristics at the junc-tion. It is found that MoTe2 forms an ohmic contact with Pd/Auwhereas a Schottky barrier is observed with Cr/Au. In addition,an excellent photo response and gate-dependent behavior wasfound for the Schottky diode. A rectication ratio of up to 103

Fig. 1 (a) Schematic illustration of the MoTe2 Schottky diode. (b) OpticaTransfer characteristics of p-MoTe2 with Pd/Au and Cr/Au FETs with Vds¼resistive metal contact effect of p-MoTe2 with Cr/Au, and (f) ultra-low r

10018 | RSC Adv., 2019, 9, 10017–10023

was calculated for the device. Furthermore, traditional therm-ionic emission theory was applied to determine the values of theSchottky barrier heights for individual metal contacts. Theresults obtained suggested that there would be useful techno-logical applications for the Schottky diodes based on MoTe2.

2. Experimental

Natural bulk crystals of p-type molybdenum ditelluride (p-MoTe2) were exfoliated with adhesive tape and a dry transfertechnique was used to transfer the akes onto silicon/silicondioxide (Si/SiO2) substrates with the help of a transparent pol-y(dimethylsiloxane) (PDMS) stamp. Multilayered p-MoTe2 nano-akes were identied using Raman spectroscopy, optical

l microscope image of the device. (c) Band profile of Pd/MoTe2/Cr. (d)0.5 V. The ID–VD characteristics as a function of gate bias, (e) ultra-highesistive ohmic metal contact behavior of MoTe2 with Pd/Au.

This journal is © The Royal Society of Chemistry 2019

Fig. 2 (a) Gate-dependent rectifying effect of MoTe2 Schottky junc-tion between Cr/Au–Pd/Au contacts. (b) Rectification ratio as a func-tion of the back gate of MoTe2 Schottky junction.

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microscopy and the results obtained were also conrmed usingatomic force microscopy (AFM). Electrodes were made using e-beam lithography by depositing Pd/Au (8/10 nm) and Cr/Au (8/10 nm), onto the p-MoTe2 FET. The electrical transportmeasurements both at room and low temperatures were per-formed using the semiconductor characterization systems,Keithley 2400 Source Meter and Keithley 6485 Picoammeter.

3. Results and discussion

The device is illustrated schematically in Fig. 1a and the opticalimage of the device is shown in Fig. 1b. The p-MoTe2 nano-akes were exfoliated from their bulk form and using a drytransfer technique with a PDMS stamp were transferred ontothe Si/SiO2 substrate. Fig. S1(a) (ESI†) shows the typical AFMimage of p-MoTe2 FET on the SiO2 substrate. In addition theheight prole for p-MoTe2 akes with a thickness of �8 nmfrom the AFM image was obtained, and the results are shown inFig. S1(b) (ESI†). Fig. S3 (ESI†) shows the Raman spectra of few-layer p-MoTe2 obtained using an excitation laser with a wave-length of 514 nm. Three peaks of MoTe2 were observed: A1gmode at �173.5 cm�1, E1

2g mode at �235.2 cm�1, and B12g mode

at �290.8 cm�1.1

Metals having larger values of work function are favorable forp-MoTe2 to form a shallow Schottky barrier whereas with lowvalues of work function they show a greater barrier height.29,30 Itwas found that MoTe2 and the metal interface could be eitheran ohmic type or rectifying in nature depending on the workfunction of both the metals and the semiconductor. Pd (f ¼ 5.6eV)31 and Cr (f ¼ 4.5 eV)32 were selected as the high and lowwork function metals, respectively, as shown in Fig. 1c.

Initially, the electrical performance of the device with source/drain Cr/Au and Pd/Au contacts was measured. For bothcongurations, p-MoTe2 showed strong p-type conduction asshown in Fig. 1d. The eld-effect carrier mobility (mFE) wascalculated for individual metal contacts using the followingequation:

mFE ¼ L

W

�dIds

dVbg

�1

CbgVds

where W and L are the channel width and length, respectively,Cbg is the gate capacitance (�115 aF mm�2) for the Si/SiO2

substrate and�dIdsdVbg

�is the slope of the transfer characteris-

tics. The hole mobility for the Cr/Au contacts was found to be1.2 cm2 V�1 s�1 with a current on/off ratio of 103 whereas thehole mobility for the Pd/Au electrodes was found to be 7.0 cm2

V�1 s�1 with an on/off ratio of around 106 at Vds ¼ 0.5 V. Thesendings revealed improved electrical characteristics when Pd/Au were contacted with MoTe2 rather than Cr/Au, which couldbe because of the formation of an ohmic contact and also bebecause of the use of a high work functionmetal (Pd with a workfunction f ¼ 5.6 eV).31 Also, in Fig. 1c it is clearly indicated inthe band prole that the Fermi level of Pd is deeper than theFermi level of MoTe2.

In addition, the ID–VD output characteristics were measuredas a function of the back gate voltage (Vbg) which illustrated

This journal is © The Royal Society of Chemistry 2019

rectifying behavior for the Cr/Au metal contacts because of theformation of the Schottky barrier with p-MoTe2 (Fig. 1e),whereas ohmic contact is formed with Pd/Au because of linearI–V characteristics as shown in Fig. 1f.

The output characteristics using Pd/Au and Cr/Au asym-metric electrodes showed a clear gate-dependent recticationbehavior, particularly at negative gate bias voltages because ofthe high Schottky barrier height between Cr and MoTe2 asshown in Fig. 2a. The forward current increased steadily asa result of thinning the barrier. The rectication ratio could bedened as the ratio of reverse current (Ir) to forward current (If)at same �Vds.33 The rectication ratio changed from 5.2 � 101

to 1.9 � 103 with variation in gate bias as shown in Fig. 2b. TheSchottky diode showed a better rectication ratio at a negativegate bias because of the reduction of the reverse leakage currentbecause of greater band banding of the semiconductor withrespect to the metal's Fermi level.21,22

Furthermore, the rectifying performance of the Schottkydiode was studied by determining the ideality factor using theShockley diode equation:34,35

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ID ¼ IS

�exp

�qV

nKB T

�� 1

�

where ID and IS are the diode and reverse bias saturationcurrents, respectively, V is the applied voltage across the diode,n is an ideality factor, q is an electronic charge, T is thetemperature and KB is the Boltzmann constant. For voltage >KBT (e.g., > 0.1 V), the previous equation becomes:

lnðIDÞ ¼ lnðISÞ þ�

q

nKB T

�V

The slope from the plot of the natural logarithm of thediode current versus the applied voltage gives q/nKBT, whichgives n. The lowermost value of n is found to be �1.4. Thetemperature dependent transfer characteristics were alsomeasured, as shown in Fig. S2 (ESI†), to extract the Schottkybarrier height (SBH) of Pd (f ¼ 5.6 eV)31 and Cr (f ¼ 4.5 eV).32

In this research, metal contacts were exclusively made of Pdand Cr and were directly adhered to the 2D semiconductor(MoTe2).

According to traditional thermionic emission theory, thefollowing equation was used:36–38

Fig. 3 (a) Conventional Richardson plot ln(I/T2) versus 1000/T for Cr/Ajunction as a function of Vbg–Vth. (c) Conventional Richardson plot ln(Iheight at the MoTe2/Pd/Au junction as a function of Vbg–Vth.

10020 | RSC Adv., 2019, 9, 10017–10023

Ids ¼ AdeviceA* T2 exp

�� q

KBT

�FB � Vds

n

��

where Adevice and A* are the area of the detector and Richardsonconstant, respectively, q is the elementary charge of the elec-tron, T is the temperature, KB is the Boltzmann constant, Vds thesource-drain voltage, and n is the ideality factor. Fig. 3a and cshow the Arrhenius plot of the device at various gate overdrivevoltages for Cr and Pd, respectively. By taking the slope of ln(Ids/T2) versus 1000/T, the SBH for Pd and MoTe2 was calculated tobe about�90 meV, whereas the extracted SBH for Cr andMoTe2was about�300meV as shown in Fig. 3b and c, respectively. Thevalue of FB (SBH), taking into consideration the Schottky–Mottrule, is the variation in metal work function (Fmetal) and semi-conductor electron affinity (csemi):

FB ¼ Fmetal � csemi.

However, a number of semiconductors differ from thepreviously mentioned rule ever since the establishment ofmetal-induced gap states,39,40 which are occupied with electronsand shi the middle of the bandgap nearer to the Fermi leveland this effect is known as Fermi level pinning.31,41 For example,p-MoTe2 had a stronger Fermi level pinning with Pd metal.31

u metal contacts. (b) The potential barrier height at the MoTe2/Cr/Au/T2) versus 1000/T for Pd/Au metal contacts. (d) The potential barrier

This journal is © The Royal Society of Chemistry 2019

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However, the barrier height between Cr and MoTe2 was higherthan that between Pd and MoTe2, which was the reason for theohmic behavior of the MoTe2 and Pd/Au junction. Underforward biasing, if the Cr metal is connected with a negativebias, forward biasing would result in the holes being attractedto the interface as a result of a decrease in barrier height.Instead, under reverse biasing, if the Cr metal is connected witha positive terminal, reverse biasing would result in the holesbeing removed from the interface of the metal and semi-conductor as a result of increased barrier height. So in theforwarding biased region the net current is larger, while in thereverse biasing region it is very low.

In addition, the photoresponse characteristics of the MoTe2Schottky diode were also demonstrated. Under forwardingbiasing the linear output characteristics were measured usingasymmetric metal contacts, under light illumination witha green laser light with a wavelength of about 530 nm havinga power of 1.2 mW cm�2 as shown in Fig. 4. At the forwardbiased region, the dark current was very low because of theultra-high resistive metal contact between Cr and MoTe2.Upon illumination with green laser light, the photo-responsivity (R) of the Schottky junction was calculated usingthe equation:

R ¼ Iph

PLaser�A

where Iph is the photocurrent and PLaser is the laser power.42,43

The calculated responsivity was 3.8 � 103 A W�1 which washigher than that previously reported for Schottky junctionsbased on conventional semiconductor materials.23,44

In addition, the Schottky diode was tested for the applicationof rectication, and which rectied output voltage signals byapplying both AC square and sine waves. Fig. 5 presents thedynamic rectied VIn–VOut curves of the device at an externalresistance of 1 MU by applying the AC sine and square inputvoltage signal sweeping from �5 to +5 V at 10 Hz.

Fig. 4 Output characteristics of the Schottky diode (Cr/Au–Pd/Au)with the positive bias as a function of gate bias.

Fig. 5 (a) Schematic illustration to demonstrate the dynamic rectifi-cation of a Schottky diode. Demonstration of rectified dynamic outputof the Schottky diode by applying (b) AC sine and (c) square wavesignals with a series resistor of resistance 1 MU. VIn ¼ �5 V at 10 Hz.

This journal is © The Royal Society of Chemistry 2019

4. Conclusions

In summary, a Schottky barrier diode was formed, based on a p-MoTe2 FET, which demonstrated excellent photo response andgate-dependent behavior. The Schottky diode showed a clearrectifying behavior with an on/off ratio reaching up to 103 andwith an ideality factor of �1.4 at zero gate voltage. In order tocheck the photovoltaic response, the diode was illuminatedwith green laser light, and the responsivity was 3.8� 103 A W�1,which was higher than the previously reported values based on

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conventional semiconductor materials. The barrier heights forPd and Cr with a MoTe2 junction were calculated to be 90 meVand 300 meV, respectively. In addition, the device was used forrectication and revealed stable rectifying behavior. Theoutcomes of this research can be applied in future electronicswhich require high speed and low noise performance.

Conflicts of interest

There are no conicts to declare.

Acknowledgements

This work was funded by the Higher Education Commission(HEC) of Pakistan under the National Research Program forUniversities (NRPU) (Project No. 7876). This research was alsosupported by the HEC of Pakistan under the Start-Up ResearchGrant Program (Project No. 1285).

References

1 O. Lopez-Sanchez, D. Lembke, M. Kayci, A. Radenovic andA. Kis, Nat. Nanotechnol., 2013, 8, 497–501.

2 C. Lan, C. Li, Y. Yin and Y. Liu, Nanoscale, 2015, 7, 5974–5980.

3 N. Perea-Lopez, A. L. Elıas, A. Berkdemir, A. Castro-Beltran,H. R. Gutierrez, S. Feng, R. Lv, T. Hayashi, F. Lopez-Urıasand S. Ghosh, Adv. Funct. Mater., 2013, 23, 5511–5517.

4 J. Klinovaja and D. Loss, Phys. Rev. B: Condens. Matter Mater.Phys., 2013, 88, 075404.

5 B. Radisavljevic, A. Radenovic, J. Brivio, I. V. Giacometti andA. Kis, Nat. Nanotechnol., 2011, 6, 147–150.

6 T. Georgiou, R. Jalil, B. D. Belle, L. Britnell, R. V. Gorbachev,S. V. Morozov, Y.-J. Kim, A. Gholinia, S. J. Haigh andO. Makarovsky, Nat. Nanotechnol., 2013, 8, 100–103.

7 S. Fathipour, N. Ma, W. Hwang, V. Protasenko,S. Vishwanath, H. Xing, H. Xu, D. Jena, J. Appenzeller andA. Seabaugh, Appl. Phys. Lett., 2014, 105, 192101.

8 C. Ruppert, O. B. Aslan and T. F. Heinz, Nano Lett., 2014, 14,6231–6236.

9 M. Yamamoto, S. T. Wang, M. Ni, Y.-F. Lin, S.-L. Li,S. Aikawa, W.-B. Jian, K. Ueno, K. Wakabayashi andK. Tsukagoshi, ACS Nano, 2014, 8, 3895–3903.

10 B. Chamlagain, Q. Li, N. J. Ghimire, H.-J. Chuang,M. M. Perera, H. Tu, Y. Xu, M. Pan, D. Xaio and J. Yan,ACS Nano, 2014, 8, 5079–5088.

11 I. G. Lezama, A. Arora, A. Ubaldini, C. Barreteau, E. Giannini,M. Potemski and A. F. Morpurgo, Nano Lett., 2015, 15, 2336–2342.

12 I. G. Lezama, A. Ubaldini, M. Longobardi, E. Giannini,C. Renner, A. B. Kuzmenko and A. F. Morpurgo, 2D Mater.,2014, 1, 021002.

13 C. Pan, Y. Fu, J. Wang, J. Zeng, G. Su, M. Long, E. Liu,C. Wang, A. Gao and M. Wang, Adv. Electron. Mater., 2018,4, 1700662.

10022 | RSC Adv., 2019, 9, 10017–10023

14 Y. F. Lin, Y. Xu, S. T. Wang, S. L. Li, M. Yamamoto,A. Aparecido-Ferreira, W. Li, H. Sun, S. Nakaharai andW. B. Jian, Adv. Mater., 2014, 26, 3263–3269.

15 D. H. Keum, S. Cho, J. H. Kim, D.-H. Choe, H.-J. Sung,M. Kan, H. Kang, J.-Y. Hwang, S. W. Kim and H. Yang, Nat.Phys., 2015, 11, 482.

16 S. Nakaharai, M. Yamamoto, K. Ueno, Y.-F. Lin, S.-L. Li andK. Tsukagoshi, ACS Nano, 2015, 9, 5976–5983.

17 Y. F. Lin, Y. Xu, C. Y. Lin, Y. W. Suen, M. Yamamoto,S. Nakaharai, K. Ueno and K. Tsukagoshi, Adv. Mater.,2015, 27, 6612–6619.

18 Y.-Q. Bie, G. Grosso, M. Heuck, M. M. Furchi, Y. Cao,J. Zheng, D. Bunandar, E. Navarro-Moratalla, L. Zhou andD. K. Efetov, Nat. Nanotechnol., 2017, 12, 1124.

19 Y. Deng, Z. Luo, N. J. Conrad, H. Liu, Y. Gong, S. Najmaei,P. M. Ajayan, J. Lou, X. Xu and P. D. Ye, ACS Nano, 2014, 8,8292–8299.

20 W. Hu and J. Yang, J. Mater. Chem. C, 2017, 5, 12289–12297.21 A. Di Bartolomeo, A. Grillo, F. Urban, L. Iemmo, F. Giubileo,

G. Luongo, G. Amato, L. Croin, L. Sun and S. J. Liang, Adv.Funct. Mater., 2018, 28, 1800657.

22 A. Di Bartolomeo, F. Urban, M. Passacantando, N. McEvoy,L. Peters, L. Iemmo, G. Luongo, F. Romeo and F. Giubileo,Nanoscale, 2019, 11, 1538–1548.

23 T.-Y. Oh, S. Woo Jeong, S. Chang, K. Choi, H. Jun Ha andB. Kwon Ju, Appl. Phys. Lett., 2013, 102, 021106.

24 Y. Zhao, X. Xiao, Y. Huo, Y. Wang, T. Zhang, K. Jiang,J. Wang, S. Fan and Q. Li, ACS Appl. Mater. Interfaces, 2017,9, 18945–18955.

25 J. Miao, S. Zhang, L. Cai and C. Wang, Adv. Electron. Mater.,2016, 2, 1500346.

26 J. B. Soole and H. Schumacher, IEEE J. Quantum Electron.,1991, 27, 737–752.

27 S. Averin, R. Sachot, J. Hugi, M. De Fays and M. Ilegems, J.Appl. Phys., 1996, 80, 1553–1558.

28 M. Yang, K. Teo, W. Milne and D. Hasko, Appl. Phys. Lett.,2005, 87, 253116.

29 M. Hughes, K. Homewood, R. Curry, Y. Ohno andT. Mizutani, Appl. Phys. Lett., 2013, 103, 133508.

30 B. Ryu, Y. T. Lee, K. H. Lee, R. Ha, J. H. Park, H.-J. Choi andS. Im, Nano Lett., 2011, 11, 4246–4250.

31 C. Kim, I. Moon, D. Lee, M. S. Choi, F. Ahmed, S. Nam,Y. Cho, H.-J. Shin, S. Park and W. J. Yoo, ACS Nano, 2017,11, 1588–1596.

32 N. Dhar, T. Chowdhury, M. Islam, N. Khan, M. Rashid,M. Alam, Z. Alothman, K. Sopian and N. Amin,Chalcogenide Lett., 2014, 11, 271–279.

33 F. Liu, W. L. Chow, X. He, P. Hu, S. Zheng, X. Wang, J. Zhou,Q. Fu, W. Fu and P. Yu, Adv. Funct. Mater., 2015, 25, 5865–5871.

34 D. A. Neamen, Semiconductor physics and devices, McGraw-Hill, New York, 1997.

35 T. Banwell and A. Jayakumar, Electron. Lett., 2000, 36, 291–292.

36 J. H. Lee, H. Z. Gul, H. Kim, B. H. Moon, S. Adhikari,J. H. Kim, H. Choi, Y. H. Lee and S. C. Lim, Nano Lett.,2017, 17, 673–678.

This journal is © The Royal Society of Chemistry 2019

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AM

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le is

lice

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e C

omm

ons

Attr

ibut

ion-

Non

Com

mer

cial

3.0

Unp

orte

d L

icen

ce.

View Article Online

37 A. Allain, J. Kang, K. Banerjee and A. Kis, Nat. Mater., 2015,14, 1195.

38 S. Das, H.-Y. Chen, A. V. Penumatcha and J. Appenzeller,Nano Lett., 2012, 13, 100–105.

39 K.-A. Min, J. Park, R. M. Wallace, K. Cho and S. Hong, 2DMaterials, 2016, 4, 015019.

40 S. Picozzi, A. Continenza, G. Satta, S. Massidda andA. Freeman, Phys. Rev. B: Condens. Matter Mater. Phys.,2000, 61, 16736.

This journal is © The Royal Society of Chemistry 2019

41 P. Bampoulis, R. Van Bremen, Q. Yao, B. Poelsema,H. J. Zandvliet and K. Sotthewes, ACS Appl. Mater.Interfaces, 2017, (46), 39860–39871.

42 M. M. Furchi, A. Pospischil, F. Libisch, J. Burgdorfer andT. Mueller, Nano Lett., 2014, 14, 4785–4791.

43 L. Ye, H. Li, Z. Chen and J. Xu, ACS Photonics, 2016, 3, 692–699.

44 A. Rochas, A. R. Pauchard, P.-A. Besse, D. Pantic, Z. Prijic andR. S. Popovic, IEEE Trans. Electron Devices, 2002, 49, 387–394.

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